scsi: hisi_sas: Run I_T nexus resets in parallel for clear nexus reset

For a clear nexus reset operation, the I_T nexus resets are executed
serially for each device. For devices attached through an expander, this
may take 2s per device; so, in total, could take a long time.

Reduce the total time by running the I_T nexus resets in parallel through
async operations.

Link: https://lore.kernel.org/r/1623058179-80434-3-git-send-email-john.garry@huawei.com


Signed-off-by: Luo Jiaxing <luojiaxing@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>